Most third-party services used unofficial Instagram APIs. The "patch" involved Meta changing the login handshake protocol. Today, if a sketchy website asks for your username/password (most free trials do), Instagram’s security system immediately sends a "Suspicious login attempt" alert and forces a password reset, breaking the bot chain.
If you’ve been looking for that offer recently, you may have noticed it no longer works. From what we can tell, Instagram has patched the loophole or third-party method that allowed it. 100 free instagram followers trial patched